The Small Current Grounding Fault Line Selection Method Research Based On Transient Information

Non-effective grounding grids could continue to run with a single-phase ground fault for1to2hours,which is very beneficial for improving the reliability of power supply. So, the distribution networks in China and many countries widely adopt Non-effective ground operation mode. As a single-phase ground fault occurs in a distribution network, the current mutation amount of the fault line could be very weak, and capacitive current arc can be used to compensate big fault current in larger capacitive current grid.A variety of factors seriously affect the small current grounding fault line selection protection selectivity and sensitivity. After years of efforts, the domestic and foreign experts in the technical aspects of small current grounding fault line selection made certain achievements. Different signal in accordance with the use of small current grounding line protection can be divided into the active selection protection and passive selection protection. Active selection protection requires additional equipment, with poor economy. Passive line selection to protect divided into fault steady-state information protection and use of fault transient two types of information protection. For the resonant grounded system, the steady-state amount of protection does not apply. Because of momentary transient fault component far outweigh the steady-state fault component, the resonant grounding operation mode, the influence of using small fault transient information protection of high sensitivity.This paper Take advantage of the fault transient information and propose two new line selection method.With the lack of theoretical analysis about Small current grounding fault line selection for, this paper based on the phase mode transformation theory, through the fault surface appearance to perceive the essence, is set up for failure analysis and transient component characteristics of the simplified model, the list of higher order circuit dynamic equation, this paper analyzes the fault current transient components, detailed research on the non effective grounding grid phase-to-ground fault occurred when the current oscillation mechanism. Finally, through the fault transient signal characteristic analysis, from essentially reveals transient characteristics of the non effective grounding grid happen single-phase earth fault.This paper introduces the basic principle of wavelet transform, has good time-frequency analysis characteristics of the wavelet transform is processing transient non-stationary signal ideal mathematical tool. Through the signal for wavelet transform method for transient component, this paper based on the zero die current and zero mode voltage of the wavelet transform modulus maxima, defines the transient amplitude and transient polarity fault measure. Put forward two new small current grounding fault line selection method:the transient amplitude and transient polarity fault measure method based on the wavelet transform. Amplitude method using fault lines zero die current wavelet transform modulus maxima amplitude is far greater than the fault lines for routing; Polarity method using fault line and the non-fault line zero die current wavelet transform modulus maxima of opposite polarity for routing. Finally, this paper established the effective grounding grid ATP simulation model. In non-ground neutral network and resonant grounding grid, change the fault point location, transition resistance and fault initial phase Angle three main influencing factors, simulate the single-phase grounding fault, calculate each line transient amplitude and transient polarity fault measure, by comparing the size to determine the fault lines, so as to verify the correctness of the two kinds of routing method.